Variable capacitor having an increased current capacity

ABSTRACT

The invention relates to a variable capacitor which, due to its particular arrangement of electrodes, enables a significantly higher current flow than generally known constructions having the same or a similar structural shape. Said capacitor also has an increased life expectancy and is compatible with existing capacitors in terms of connection. Such variable capacitors can be used in high frequency generators, in matchboxes and in interface networks for industrial high frequency applications, as regulatable filters in high frequency power electronics and in the power part of emission installations.

The invention relates to a variable capacitor with increased currentcarrying capacity according to claim 1 and applications according toclaims 11 and 12.

Variable vacuum capacitors usually have a metallic spring bellow that,on the one hand, conducts the current from the electrode with which itis electrically connected to the external contact points and, on theother hand, represents a mechanically deformable dividing wall betweenthe vacuum present around the electrodes and the external atmosphericpressure. To achieve a long lifespan, i.e. enable as many movementcycles as possible, the bellow material must be selected so that it hasgood mechanical properties. On the other hand, it must have goodelectrical conductivity in order to minimize electrical losses and toavoid unnecessary heating, which again may have a negative effect onmechanical long-term behavior. However, the necessary structure of thebellow folds also results in long current paths, leading to an increasedelectrical series resistance and increased series inductance.

U.S. Pat. No. 3,611,075 introduces a variable vacuum capacitorcharacterized by a low inherent resonance frequency and provided with aunilateral, electrical connection for coaxial lines. It isapplication-specific, i.e. determined by an application. It alsocomprises three insulator parts, which makes for a complex constructionand is also a disadvantage.

It is the objective of the invention to describe a variable capacitorthat, in comparison to previous versions and sizes, permits a markedincrease in electric current carrying capacity combined with lifespanvalues several times higher than previously known. Another objective ofthe invention is to design the shape of the variable capacitor in such away as to allow replacement of an existing version, so that animprovement of the performance characteristics of an existingapplication can be sustained in a simple manner.

According to the invention, this objective is realized with a variablecapacitor according to the wording of claim 1 and applications accordingto claims 11 and 12.

The invention is described below with the help of drawings. In thesedrawings:

FIG. 1 shows a sectional view of a schematic illustration of a variablecapacitor with increased current carrying capacity according to theinvention;

FIG. 2 shows a first embodiment of a connection-compatible, variablevacuum capacitor;

FIG. 3 shows a second embodiment of a variable vacuum capacitor with asmall, lower connection ring;

FIG. 4 shows a third embodiment of a gas-filled, variable capacitor withan insulator as part of the housing bottom.

FIG. 1 shows a sectional view of a schematic illustration of a variablecapacitor with increased current carrying capacity according to theinvention.

A variable capacitor 20 with a housing bottom 13 and a connection 14arranged on the outside of the latter in an electrically conductivemanner has on the inside of the housing bottom 13 an inner electrode 11connected with the latter in an electrically conductive manner, saidinner electrode being part of a fixed electrode part. The housing bottom13 transitions at its outer limit into a cylindrical housing, to whichthe lower side of an insulator ring 7 is attached in a gas-tight manner.On the top of the insulator ring 7 is located a cylindrical housingjacket 5, also attached in a gas-tight manner, that is terminated at itstop end by a housing cover with a connection 2 attached to its outsidein an electrically conductive manner. The housing cover has in itscenter an opening for an adjustment device 1 that guides a variableelectrode part in a sliding manner by way of a guide device 3. The guidedevice 3 is connected by way of a spring bellow 4 with the inside of thehousing cover. The space between the housing jacket 5 and the springbellow 4 is used for evacuation or for filling with gas. The variableelectrode part, consisting of an inner electrode 9 and an outerelectrode 10 connected galvanically and mechanically with the former isconnected via an insulator 6 with the adjustment device 1. The innerelectrode 9 comprises a plurality of electrode elements or electrodeplates arranged concentrically or helically around the center axis ofthe capacitor. By way of the adjustment device 1, they are able to dipinto the electrodes of the fixed electrode part. The housing jacket 5continues above its attachment at the insulator ring 7 on its inside ina conductive manner with an inner jacket ring 8, at the lower end ofwhich an outer electrode 12 is attached, which is part of the fixedelectrode part. In this way, the housing jacket 5 is mechanically andelectrically connected with the outer electrode 12. The outer electrode12 comprises a number of electrode elements or electrode plates thatsurround the center axis of the capacitor concentrically or helically,but which are arranged galvanically and mechanically separated from theinner electrode 11 of the fixed electrode part.

The electrode elements 9, 10, 11, 12 also may be constructed helically.

Because the outer electrode 12 of the fixed electrode part is fed viathe upper connection 2, the housing jacket 5, and the inner jacket ring8, the spring bellow 4 remains current-free, since the insulator 6ensures the galvanic separation of the guide device 3 with spring bellow4 from the variable electrode part with electrodes 9, 10.

By directing the electrical current lines on paths outside of the springbellow 4, the spring bellow material can be optimized according topurely mechanical aspects. The electrical current then is able to flowon a metallic path that is even more advantageous for the high-frequencycurrent. As a topological consequence of this, the electrode packetsmust be designed so that the adjusting element for the variableelectrode part with electrodes 9, 10, including the spring bellow 4,remains current-free. This means that the spring bellow is not heated,which protects the material. This can be achieved in that the variableelectrode part or the adjustable electrode assumes an electrical bridgefunction, said bridge, for the purpose of adjusting the capacity of thecapacitor, being immersed more or less deeply into two additional,galvanically separated electrodes that are part of the fixed electrodepart. The two last mentioned electrodes 11, 12 then may be connected viamechanically rigid, electrical connections with the connection points orconnections of the capacitor. With the two connections 2, 14 of thecapacitor, the latter can be constructed so that it is 100% able toreplace generally known constructions of same or similar design. This isespecially advantageous for refitting purposes.

The design of the electrodes is widely variable. For example, theelectrode elements of the electrode 11 of the fixed electrode part mayhave different heights with respect to each other, resulting in novelcapacity behaviors within the adjustment range, which are not describedin detail here. It is, however, preferred that the electrode elementsare of the same height.

One construction with electrode elements of different heights, asdescribed for electrode 11, also applies to the other electrodes 9, 10,and 12 or parts thereof.

According to the invention, the increase in current load capacity is20-30% with a simultaneous five-fold increase in lifespan; this meansthat up to 5 times as many cycles can be performed.

The described construction of such a variable capacitor appliespreferably to vacuum capacitors, but is principally also valid forgas-filled capacitors.

FIG. 2 shows a first embodiment of a connection-compatible, variablevacuum capacitor. The shown variable vacuum capacitor essentiallycorresponds to the construction of the capacitor according to FIG. 1 andhas the following differences. The insulator ring 7 has a diameter of 90mm and a cross-section of 20×7 mm with an overall capacitor height of130 mm and is located at a small distance above the housing bottom 13.The housing jacket 5 is constructed longer, there is no inner jacketring, and the outer electrode 12 of the fixed electrode part is attachedjust vertically above the insulator ring 7 of the housing jacket 5. Thecapacity is 500 pF, and the permissible voltage is 10 kVpt (peak test).

Connections 2 and 14 for electrodes 12 and 11 are produced in ring shapewith outside diameters of 70 mm or 35 mm respectively, so that ittherefore has a connection geometry like existing variable vacuumcapacitors with an overall height of 130 mm and easily can replace them,i.e. is connection-compatible.

FIG. 3 shows a second embodiment of a variable vacuum capacitor with alarge lower connection ring.

The shown variable vacuum capacitor essentially corresponds to theconstruction of the capacitor according to FIG. 2. It has the followingdifferences. The insulator ring 7 is a ceramic ring with dimensions of80×15 mm. The insulator 6 is a ceramic ring with an outside diameter of40 mm and a cross-section of 15×5 mm. Its overall height is 120 mm. Thecapacity is 800 pF, and the permissible voltage is 5 kVpt (peak test).The connection 14 for electrode 12 is produced in ring shape with anoutside diameter of 70 mm, so that it therefore also fulfills therequirements of a connection geometry of existing vacuum capacitors withan overall height of 120 mm and is fully connection-compatible withthem.

FIG. 4 shows a third embodiment of a gas-filled, variable capacitor withan insulator as part of the housing bottom.

The shown, gas-filled variable capacitor essentially corresponds to theconstruction of the capacitor according to FIG. 2. It has the followingdifferences. The insulator ring 7 is constructed in disk shape and ispart of the housing bottom 13. It has an outside diameter of 80 mm and across-section of 5×15 mm. The capacitor has an overall height of 120 mm.The capacity is 1000 pF, and the permissible voltage is 5 kVpt (peaktest). The connection 14 for electrode 11 is produced in ring shape withan outside diameter of 52 mm and has a cross-section of 1.5×13 mm. Astandard gas filling is located in the space between the spring bellow 4and the housing jacket 5.

The advantages of the variable capacitor according to the invention areits higher current load capacity along with a several times higherlifespan. Previous solutions involving compromises between electricaland mechanical requirements are no longer necessary. In addition, it maybe produced with identical construction, i.e. an identical or at leastvery similar housing appears to be beneficial, enabling a simple upgradewith respect to higher HF current, higher HF power, and longer lifespanof an already existing equipment construction.

New constructions in which such a capacitor is used can be designed forhigher HF currents and powers without requiring greater dimensionsthemselves.

Smaller electrical path resistance values result in reduced electricalpower losses, which result in a higher total efficiency. Shorterelectrical current paths also result in reduced serial inductivity,which expands the application range for vacuum capacitors far into theVSW range (>150 MHz).

It is found to be particularly advantageous that the spring bellow iskept current-free with only one second insulator at the variableelectrode part.

Such capacitors are used in high-frequency generators and matchboxes andmatching networks for industrial HF applications, as adjustable filtersin HF power electronics, and in the power unit of transmitting stations.

It is essential for the invention that the capacitor according to theinvention, due to its special arrangement of the electrodes, permits adistinctly higher current flow than generally known constructions, thatit is simultaneously characterized by an increased lifespan, and that itis connection-compatible.

1. Variable capacitor, comprising a fixed electrode part and a variableelectrode part, a housing bottom, an insulator ring, a housing jacket, aspring bellow, and an adjustment device, wherein the fixed electrodepart consists of an inner electrode and an outer electrode galvanicallyseparated from the former; wherein the variable electrode part consistsof an inner electrode and an outer electrode connected galvanically withthe former; wherein the variable electrode part is connected via aninsulator with the adjustment device, and the latter is connected by wayof the spring bellow in a gas-tight manner with the housing jacket;wherein the housing jacket is separated from the housing bottom by aninsulator ring; and that wherein the inner and outer electrodes of thevariable electrode part are arranged so as to be able to slide by meansof the adjustment device via a guide device and able to dip into theinner and outer electrodes of the fixed electrode part, whereby thespring bellow is current-free.
 2. Variable capacitor according to claim1, wherein the outer electrode of the fixed electrode part iselectrically connected with the housing jacket, whereby the latter hason the top a connection of the outer electrode through which one powersupply is accomplished, while the inner electrode of the fixed electrodepart has a lower connection through which the other power supply isaccomplished.
 3. Variable capacitor according to claim 1, wherein theouter electrode of the fixed electrode part is electrically connectedwith the housing jacket by way of an inner jacket ring.
 4. Variablecapacitor according to claim 1, wherein it has an externally identicallyconstructed form with respect to existing variable capacitors andtherefore can replace them or is connection-compatible with them. 5.Variable capacitor according to claim 1, wherein the electrode elementsof the electrodes consist of concentrically arranged individualelectrodes.
 6. Variable capacitor according to claim 1, wherein theelectrodes are arranged concentrically with respect to each other. 7.Variable capacitor according to claim 1, wherein the electrodes consistof helically arranged electrode elements or of individual electrodes. 8.Variable capacitor according to claim 7, wherein the electrodes arearranged concentrically with respect to each other.
 9. Variablecapacitor according to claim 1, wherein the outer electrodes (10, 12)have a different electrode height than the inner electrodes, butpreferably have the same height.
 10. Variable capacitor according toclaim 1, wherein the electrode elements of the electrodes have adifferent electrode height with respect to each other, but preferablyhave the same height.
 11. Use of the variable capacitor according toclaim 1 in high-frequency generators and matchboxes and matchingnetworks for industrial HF applications.
 12. Use of the variablecapacitor according to claim 1 in adjustable filters in HF powerelectronics and in the power unit of transmitting stations.